The present invention relates to a method for thermal decomposition treatment of a radioactive waste generated in a nuclear fuel reprocessing plant and a nuclear power plant, which method can recover a stabilized radioactive solid of reduced volume as a residue by decomposing, vaporizing and removing sodium compounds contained in the radioactive waste.
High-level liquid waste generated from a nuclear fuel reprocessing plant contains sodium compounds, nuclear fission products, actinides, corrosion products, and the like. Such a high-level liquid waste is generally processed by heating it with a heater to evaporate liquid components and to obtain a dried matter, then adding and mixing a glass forming agent and heating and melting the mixture to form a vitrified product.
In order to treat medium- or low-level liquid waste, solidification treatment by the use of a plastic forming agent and a bitumen forming agent has been carried out.
According to the solidification treatment techniques described above, various forming agents which are non-radioactive are added to the original radioactive waste and this results in a serious drawback in that the quantity of the finally processed product increases. There is a limit to the amount of sodium that can be contained in glass in order to form a vitrified product excellent in properties. Therefore, when the high-level liquid waste is subjected to the solidification treatment, it cannot be converted easily to a stable vitrified product. For further stabilization, a greater amount of the glass forming agent must be added, which disadvantageously brings about an increase in the amount of waste.
Moreover, once the solidified product is formed by adding the forming agent, it becomes extremely difficult to extract useful elements contained therein in future and effective utilization of resources cannot be made.
For the reasons described above, a technique for drastically reducing the volume of the radioactive waste and a technique for converting radioactive waste to a stable solid without adding various forming agents has been earnestly sought.